The present invention relates generally to an x-ray beam collimator assembly, and, more particularly to a collimator assembly that can be manufactured as segments and assembled into larger collimators.
Computed tomography has been utilized for a wide variety of imaging applications. One such category of applications is comprised of medical imaging. Although it is known that computed tomography may take on a wide variety of configurations within the medical industry, it commonly is based on the transmission of low energy rays (x-rays) through a body structure. These low energy rays are subsequently received and processed to formulate an image, often three-dimensional, of the body structure that can by analyzed by clinicians as a diagnostic aid.
The reception of the low energy rays, such as x-ray photons produced in an x-ray tube, is often accomplished through the use of a device referred to as a scintillator camera or detector array. The scintillator camera or detector array is typically comprised of a plurality of structures working in concert to receive and process the incoming energy rays after they have passed through the body structure. The scintillator element is commonly a material with the ability to absorb the x-ray photons and convert their energy into light. This allows the low energy rays received by the scintillator camera to be converted into useful information. Scintillator elements may come in a wide variety of forms and may be adapted to receive a wide variety of incoming rays. The light produced by the scintillator element is commonly processed by way of a device such as a light sensitive photodiode which converts the light from the scintillator element into an amplified electronic signal. In this fashion, the information from the scintillator camera can be easily transferred, converted, and processed by electronic modules to facilitate viewing and manipulation by clinicians.
A collimator is an element often found in a scintillator camera that is used to limit the direction of photons as they approach the scintillator detecting element. The collimator is commonly used to increase the signal to scatter rejection ratio and magnification of a viewed object or control resolution or field of view. Their primary purpose, however, is to control the photons impinging on the scintillator element. The collimator components often consist of a matrix of tungsten plates. These elements must be aligned with the scintillator and the x-ray focal spot of the x-ray source. The height of the collimator elements in the y-direction (direction along the x-ray beam) is critical for scatter rejection. This scenario presents the following challenges when using the state of the art technology, where plates are used to reject scatter in one direction: Plate bow along the z-direction (along the axis of the patient in CT system) is often realized. Alignment of the scintillation detector array (often referenced as a pack) to the collimator in both x and z-directions (perpendicular plan to the direction of the x-ray beam) can be difficult. Focal alignment of the plates can be difficult and costly. Improper manufacturing can result in undesirable sensitivity to focal spot motion.
The concerns with collimator construction are further increased as longer z-direction images are desired, especially for volumetric computed tomography (VCT). As volumetric imaging gains prominence, larger collimator elements are often required. Manufacturing limitations, however, often present significant challenges to such larger collimator elements. As collimator size increases, plate bow, dimensional accuracy, and alignment can all begin to negatively impact collimator and detector performance. Although high precision manufacturing, fixturing, and precision features can at least partially address these concerns, they often are associated with undesirable cost increases. One approach is to manufacture the collimator in a series of individual modules that may be assembled prior to installation in the imaging system. The interface between adjoining modules, however, can become difficult to shield. The edge between modules can become unshielded and negatively impact the resultant image produced by the imaging system.
It would, therefore, be highly desirable to have a collimator assembly that could be manufactured in a modular/segmented fashion and thereby improve dimensional tolerance and precision features. It would additionally be highly desirable to have a modular collimator assembly with improved assembly properties such that proper shielding can be maintained.